feat(ics): import UI — open/receive .ics, 1-vs-many routing

Completes v2.7 Branch 2. Wires the import core into the app:

- Manifest ACTION_VIEW/SEND for text/calendar; MainActivity parses the
  incoming Uri (content/file only, so calendula:// deep-links don't match)
  and routes it through RootScreen → CalendarHost like the other one-shot
  intents.
- ImportViewModel reads + parses the file and routes by count: one event →
  the prefilled create form for review (EventEditViewModel.openImported,
  which freezes the reminder default so the file's reminders win); many →
  ImportScreen with a writable-calendar picker, then a bulk import (UID
  dedup) and a result summary.
- ImportScreen also surfaces parser warnings (skipped recurrence overrides,
  ignored attendees, unknown-timezone fallback). Strings EN+DE.

Package is ui.imports (not ui.import — Java keyword). lint + test +
assembleDebug green. No v2.7 tag until on-device review.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -13,10 +13,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Back up your local (device-only) calendars: Settings → Calendars → Export as
   `.ics` file writes every event of your on-device calendars to a file you
   choose. Local calendars aren't synced anywhere, so this is their only backup.
-  (Importing `.ics` files back in lands in the next update.)
-
-_Note: new events now carry a unique identifier so a future `.ics` import can
-recognise them and avoid duplicates._
+- Open or share an `.ics` file into Calendula: a single event opens the create
+  form prefilled for review, while a file with many events (e.g. a backup) opens
+  a bulk import — pick a calendar and import them all. Re-importing a backup
+  won't create duplicates (events are matched by their unique identifier), and
+  anything Calendula can't represent (changed recurring occurrences, guest
+  lists) is reported rather than silently dropped.
 
 ## [2.6.0] — 2026-06-18